The present invention relates to an apparatus for controlling an internal combustion engine such as a gasoline engine used for a motor vehicle, and, more particularly, to an apparatus for accurately controlling an air-fuel ratio of an internal combustion engine.
In the operation of an internal combustion engine such as a gasoline engine, it is preferred that the mixing ratio of air and fuel of the air-fuel mixture, i.e., the air-fuel ratio, is maintained exactly at a desired level.
In an ordinary internal combustion engine such as an gasoline engine of a motor vehicle, the intake air flow rate is controlled directly by a throttle valve mechanically connected to an accelerator pedal, and the fuel is metered mechanically by a carburetor or electrically by an electronic fuel injection controller in accordance with the intake air flow rate so as to attain the desired air-fuel ratio.
This conventional method of air-fuel ratio control has the drawback in that the desired air-fuel ratio is not attained, particularly in the transient period of the control because the change in the fuel supply rate cannot follow-up the change in the intake air flow rate due to a difference in the inertia, i.e., the specific gravity, between the air and the fuel such as gasoline. More specifically, the mixture temporarily becomes too lean when the engine is accelerated and too rich when the engine is decelerated, resulting in deviation from the air-fuel ratio aimed for.
The conventional control method explained above may be referred to as "intake air flow rate preferential type" or "follow-up fuel supply rate control type". In order to avoid theres drawbacks, U.S. Pat. No. 3,771,504 proposes a control system which may be referred to as "fuel supply rate preferential control type" or "follow-up intake air flow rate control type".
Under these circumstances, the object of the present invention is to provide an improved control apparatus of the "fuel supply rate preferential control" type for enhancing the control precision and response characteristics of the air-fuel mixture supply system, thereby ensuring a good air-fuel ratio control.
In accordance with advantageous features of the present invention, an engine control apparatus of fuel supply preferential control type is proposed wherein the rate of fuel supply is controlled in accordance with the amount of operation of an acceleration pedal and the operation condition of the engine, and the opening of the throttle valve is controlled in accordance with a command opening which is determined by the rate of the fuel supply, with the control apparatus comprising a first closed loop control means adapted to detect the throttle valve opening and to effect a control to make the throttle valve opening converge at the command opening, and a second closed loop control means adapted to detect the air-fuel ratio of air-fuel mixture fed to the engine by detecting oxygen concentration in exhaust gases from the engine and to effect a control to make the air-fuel ratio converge at a command air-fuel ratio.
The engine control apparatus further includes means for controlling the command opening so that the commencement of the operation for controlling the throttle valve opening is delayed in accordance with the engine conditions, and the changing rate of the command opening is controlled in accordance with the engine conditions at the time of acceleration or deceleraion.